In many industrial and municipal waste systems, wastewater which is laden with grit is pumped from a primary recovery device in the waste stream to a secondary device (e.g., a cyclone separator) which further concentrates the grit. The stream may also pass through a third device (e.g., a screw conveyor) to further dry and concentrate the grit.
Grit removal systems such as grit extractors or grit traps have been used in many waste systems to remove grit from the waste water prior to passing the water on to a recovery device of the system. For example, one advantageous apparatus includes flumes for injecting and extracting liquid tangentially relative to a round chamber, creating a circular flow stream which causes the grit to settle near the bottom center of the round chamber. That grit in the injected liquid is thus removed from the liquid stream and collected in the storage chamber for relatively easy removal. Such an apparatus is disclosed in U.S. Pat. No. 6,811,697 B2.
U.S. Pat. Nos. 3,941,698, 4,107,038 and 4,767,532, 7,971,732 also disclose vortex-type grit extractor apparatuses. U.S. Pat. No. 4,767,532, for example, discloses an apparatus for removing grit in which a grit storage chamber is provided beneath the center of the round chamber of the grit removal system. A removable plate substantially aligned with the floor of the round chamber generally separates the two chambers, with a central opening through the plate permitting communication between the chambers. A cylindrical shaft is rotatably supported on its upper end above the round chamber and extends down through the round chamber through the plate central opening. Liquid flow in the round chamber forces grit particles to settle toward the chamber floor, where they are urged radially inwardly so as to drop through the plate central opening into the grit storage chamber. A multi-bladed propeller is mounted on that shaft above the plate, and rotates with the shaft to assist in the liquid flow to move the grit toward the plate center opening. A pipe also extends down through the cylindrical shaft into the grit storage chamber, and a pump is provided on the upper end of the pipe to allow grit in the bottom of the storage chamber to be removed by pumping up through the pipe.
The disclosures of all of these patents are also hereby fully incorporated by reference.
Operation of such grit removal units depend on removal of grit from the waste water as the water flows from the influent channel around the round chamber to an effluent channel.
Further, since the flow of wastewater with such grit is not constant or uniform, a wide range of low to high flow rates need to be accommodated over the life of the unit. Given such a potential range of flow rates, in which the influent channel needs to be able to handle high flow rates, problems can be encountered with low flow rates. For example, when flow rates are encountered which are much lower than the design rate of the grit removal apparatus, the velocity of the influent channel is significantly reduced at such low flow rates and undesirable premature settling of grit in the influent channel can occur. Where such low flow rates are encountered over a long period of time, this can result in grit undesirably settling and remaining in the influent channel for long periods of time, until a significant flow event occurs which is capable of lifting and flushing the grit to the chamber for removal.
The present invention is directed toward overcoming one or more of the problems set forth above.